i feel hopeless

to start this off i will say i am not diagnosed with a chronic illness, though doctors are suspicious and testing for numerous autoimmune diseases and POTS. i'm fifteen and all my life there has been something wrong with me medically. i hate it. as of late it's been problems with my chest/breathing. i have popping sensations whenever i get too active and i just feel hopeless. i struggle with numerous mental health problems and for the past few years i've really wanted to be athletic and do sports to hopefully improve, but these mysterious illnesses make it hard to find something that works. my entire life i've been told "oh, you have so much potential sport wise" and i'm just so so disappointed. i want to be able to play sports. i want to run track without immediately feeling like i can't breathe. i don't want to sit on the bench just to get dizzy standing up the second i get a chance to play. i just feel sad and wanted to ramble about it to people who didn't know me personally. i apologize if this is the wrong sub for this, especially as i'm not diagnosed.